In the galvanization process, zinc is heated and maintained in a molten state within a furnace or kettle for coating steel. The temperature required is approximately 500.degree. C. (approximately 930.degree. F.). The furnace or kettle is a vital part of the galvanization process because the metal must be maintained at a constant elevated temperature to insure proper coating and the structure and operation of the kettle directly affect the quality of the resulting coating.
Generally, zinc has been heated and melted in iron kettles by applying heat externally to the kettle walls. However, zinc has a tendency to amalgamate with the iron of the kettle, causing the kettle walls to weaken. The product of this reaction, known as dross, is undesirable. Further, the presence of chlorides in the zinc accelerate the chemical reactions between the iron kettle and the zinc. These reactions cause premature kettle failure, which greatly increases the cost of galvanization. Besides the production kettle, holding furnaces used to store the molten zinc when the production kettle is being repaired suffer the same problems.
Merely lining the furnaces and kettles with refractory materials has not been a satisfactory solution, because heating through refractory walls is inefficient and the high temperatures applied to the walls cannot be withstood over extended periods of time.